Art of telephony.



n. mppnnnnBL ART OF TELEPHONY.

APPLIUA TIOI FILED lUGL 2, 190 5.

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PATENTED MAR .'13,l9'O 6-. I

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- PATBNTED MAR. 13, 1906-, D. M. THERRELL. 1

' ART OF TELEPHONY. IAPPLIOATION FILED we. 2, 1905.

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PATENTED 13, 1906.

I D. M. THERRELL.

ART OF TELEPHONY. PLIOATION FILED ,LUG. z, 1905.

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'UN TT- ED s ATEs DANIELI-MACLAUCHLIN THERRELL, OFCHARLESTONISOUTH(JAltOLINAf PATENT ,orrron ART OF TELEPHONY;

Specification of Letters Patent.

, Patented March 13, 1906.

Original application filed July 23, 1904, Serial No. 211M6- Divided. andthis application filed August 2,1905. Serial No. 272,375.

To all whom it may concern: 7

Be it known thatAI, DANIEL MACLAUCHLIN I THERRELL, a citizen of, theUnited States, re-

fro

siding at Charleston, in the'county of Charlesvented new and usefulImprovements in the Art of Telephony, of which the following is aSpecification.

My invention consists in an improved method or system a for thetransmiss on of electrical energy by means of electrical waves,

and articularly such waves-as are employed in te electrical transmissionof articulate speech or sonorous sounds, and comprises variouslmprovements to be hereinafter more particularly described and,claimed'.

' In the transmission of a simple electrical wave over anelectricalconductor of great length characterized by high resistance, elec- ,trostatic and conductive leakages, the. energy lost or dissipatedisproportional to and expressible in simple terms of the reactive-con-Qstants of the system, and there is no di'stor ;tion of thewave form..Such, however, is

not the case for a complex electrical Wave composed of a pluralitofcoexistingwaves, such as the waves invo ved in the tele honictransmissionof the human voice or ot er sonorous sounds composed of aprime or fundamental and .an' ascending series of partials correspondingto' the overtones or characteristics of articulation and quality. In thelatter case each constituent wave of the series is difierently andindependently affected, and

hence the resultant wave form at the distant end or terminusoff-transmission 1s no longer identical with the initial wave form im-'.pressed'upon the conductor. This is due to the physical fact that eachwave'is oppositely as well as difierently affected by theelectromagnetic and electrostatic constants of the system, though bothcons ire to discriminate in favor of the lower w 'le retarding orattenuating vthe upper harmonics die rectly as the frequency,resultingin the loss of articulation and the natural characteristics ofspeech which are dependent upon thetion' of the main-line conductors,owing to their electrical characteristics as outhned transmission of theupper harmonics or over:

tones, and while conceding that. great losses are properly chargeable tothe dissipaabove, my'researches. of the subject, mathematical andexperimental, have confirmed me in the opinion that, in so'far as longaerial lines are concerned, operating under, actual -conditions,.whichmight be called existing meteorological conditions, little, if anythingof average and permanent value 1s to be I obtained by a tuningorreadjustment of the ton and Stateof South Carolina,'have inline'constants,-but that much may be gained by improving the methods andapparatus in use for the electrical transformation and transmission ofthe primary energy equivalents of "the voice'that. is, by reducing theimpedance of the primary coil and obtaining thereby larger primarycurrents, by maintaining'a higher mutual inductance and obtainingthereby a hi her e'llicicncy of transformation, and by so a( j'ustingthe secondary system as to generate a larger line current at a highertransmission may be effected.

In the art of telephony a primary circuit effective line potential ahigher e'l-Iiciency ofconsists of a circuit including a variableresistance 1n rclatlon to a dlaphragm, a source of electrical energy,and the primary winding of an induction-coil or transformer Thevibrations of the voice acting upon the diaphragm n operative relationto the variable resistance causes this resistance to vary in consonancetherewith, thereby setting u in the primary c1rcu1t a current whlch folows the variations of the said resistance, and therefore the vibrationsof the voice; This cur rent beingof the variable or pulsating type iscapable of transformation by means of an 1nduction-coil or transformerthe, rimary of which 1s included 1n c1rcu1t W1th t e ordinary variableresistance and source of energy,

while the secondary is connected into the main line. By this means it ispossible, even with thesmall current to which We are re-.'

stricted by the transmitter, to so step up the voltage impressed uponthe main line as to reach over relatively vast distances; butin sayingthis it must be admitted that such results speak far more for thesensitiveness of the receiver than for the efliciencyof transformationor transmission, for though ordinarily we may have flowing in theprimary;

circuit'something like .3 oi, an ampere the maximum value of the,current impressed upon the main line is not more than .0001 of an amperefor the lowest frequency, ,with a .far greater loss in transformationforthe higher frequencies. 1

rod

'- In orderto successfully effect the long-dis- -tance transmission ofspeech, the prlme-req'uisite must be an increased power orwatt efii- IIOciency of the system for each and every fr quency involved, andparticularly for such power factor of the system is, first of all, de-

pendent upon the amount of energy available in the primary circuit.Unfortunately we are here restricted to a very small amperage on accountof the PR loss in the variableresistance portion of the transmitter,which causes the transmitter-electrodes to heat, and

thus directly affect the transmission to such an extent as to place theavailable current limit considerably below one ampere, as mentionedabove. This is not the only difficulty. Long-distance transmission makesit necessary to raisethe line potential by transformation. Anything likeefficient transformation presupposes a maximum mutual induction. This inturn calls for a high magnetic inductance, which is only possible by theuse of iron in the magnetic circuit. Now there are two paramount reasonswhy neither of these requisites are admissible in telephony. If weendeavor'to increase the magnetic intensity of the coil by the use of anincreased amount of iron in the core, we are met with a loss due to. anovcrsaturation of the core. This results from the direct current used inthe primary circuit, which saturates the core and leaves no margin forthe variation of the lines of force due to the variations in the primarycurrentfollowing the vibrations of the voice, and hence a loss in thesecondary instead of a gain. In addition there are hysteresis losses dueto high frequencies and magnetic density. Again, just in proportion tothe amount by which We increase the mutual induction of the coil by anincreased efficiency of the magnetic field we also increase theselfinduction of the primary, and therefore its effective Impedance,which means a proportional reduction of primary current unless thevoltage be raised, Even if this be done the primary current is onlyincreased at the expense of the power factor, for the wattless componentof the primary will be so great that the point is soon reached where theheating of the transmitter-electrodes makes a a larger currentimpracticable Without having improved the efficiency of the system. Thiscalls for a compromise and also throws light upon what has been to manyfor years the stated above, that to attempt a further inv paradox of theart. I refer to the constants and proportions of the standardlong-distance induction-coil as used by the American Telephone andTelegraph Company. In this coil a minimum of ironis used and thecoefficients of selfand mutual induction are.

amazingly low.- This of course means low efficlency; but experience hasshown, as

crease in the efficiency of transformation but invites other losseswhlch outwelgh any 'apparent gains. Hence the standard cigarcoil and theattempt to force the problem by searches, experimental and mathematical,

form the basis of my invention, which will be better understood byreference to the accompanying drawings, which form a part of thisspecification. I

Figure 1 is a polar diagram of a standard telephonic transformer orinduction-coil having the maximum amount of core-iron, mutual andself-induction, allowable in practice, with secondary on short circuit.Fig. 2 is an enlarged portion of Fig. 1 with eight thousand ohmsinsecondary circuit, showing the method of neutralizing the primaryself-induction by a capacity reactance. Fig. 3 is a set of curves, drawnto rectangular coordinates, showing the impedance of a primary circuitof given constants for different p. p. s., also the values ofthe imedance for the same circuit wherein the se 'inductancc is neutralized bycapacities corresponding to the given p. p. s. Fig. 4 is a set of curvesshowing the values of current for the same circuit and p. p. s. as shownin Fig. 3, together with the values of the current after aneutralization of the self-inductance by capacities corresponding to thegiven p. p. s., also curves showing the resultant secondary-currentvalues when two or three such circuits tuned to different p. p. s. areconnected in multiple, primary, and secondary. Figs. 5 and 6 are vectordiagrams showing the method of graphically determining the resultantvalues of secondary current and phase relation under the multipleconditions noted in reference to Fig. 4. Fig. 7 is a diagramillustrating the method of placinga capacity in series with the primarycoil and transmitter for the purpose of tuning. Fig. 8 is a diagramillustrating the principle and method of using com ensating-transformersin the main line for t e purpose of reducing secondary effectiveimpedance and increasing the efiective line potential. Fig. 9 is aconventionaldiagram of my system in theory as applied to local-batterysystems. Figs. 10 and 11 are conventional'diagrams of the same adaptedto common-battery or central-energy systems.

Inasmuch as the principles underlying my invention involve aconsiderable departure from the standardpractices'of the art, it willlight and the specification rendered more intelligible. Let us considera current flowing in a single turn of w1re. A magnetic field 1s setup'consisting of a definite amount ofmagnetic flux or lines of forceforming closed curves around the given conductor. This flux increasesand decreases with increase and decrease of current. If the permeabilityof' the medium is constant, the magnetic flux is directly proportionalto the current. If there are s turns of wire instead of one, the flux Npasses through each turn, and consequently there are sN lines threadingorflinked'with the circuit. Thequantity sN may be termed the.flux turnsor inductance. of the circuit. If the magnetic induction through anycircuit be changed. due to any cause whatsoever, an electromotive forces developed in I the circuit-proportionalto the rate of change of the manetic induction, as first shown ex-' perimentafl the induction to whichthis induced electromotive force is due may be producedbya change in thecurrent flowingin the circuit itself, in which case the electromotiveforce so induced is dependent upon the rate of change of thecurrent andis known asthe electromotive forceof self induction. .Le't

us now consider two coils in juxtaposition, which we will designate asprimary and secondary, each with a given number of. turns orconvolutions. Let therebe'a current of given intensity flowing in theprimary coil. This current in the primary it caused to vary produces amagnetic induction which varies inconsonance therewith." Now thisinduction not only induces an electromotive.

force of self-induction in the primary itself, but also induces anelectromotive force in the secondary, due to the ,chan ing lines offorce of the primary and the re ative position of' the two coils, whichisproportional to the. rate of change'of the induction in the primary.-This is mutual induction. This mu- I tual induction may be defined asthe. ratio of electromotive force induced in one circuit to thetime-rate of change of the current" in the other producing :it. Itmay'also' be expressed in terms ofthe induction threading.

the secondary, due to the current in the primary beingl equal to therate of change of the number of inesof force linked with the secondary.The efiect is greatly increased by the use of ironinthemagnetic circuit.Upon these principles is based the operation of the devices used forchanging an alternating orvarying current from one potential to an.other of. higher or lowerpressure, known as i induction-coilsortransformers. J In or.

der to determine the action between the primary and secondary circuitsof a transformer throu h the medium of their common Imag netic el d, wemust ascertain thearnount of induction due to the currentflowin throughthe turns of the primary and em raclng a ly by Faraday- The change inmagneticcircuit of, known permeability.

This may be readily calculated from the laws of the ma netic circuit.The'total magnetic fluX or induction N is equal to the magneto- 1not1veforce divided by the reluctance. The

secondary:electromotive force induced by the primary current isproportional to the rate at which'the primary current is changing and isequal to this time-rate of chan e multiplied Subscripts 1 and 2 refer toprimary and secondary circuits,

this specification.- Having briefly respectively, throughout outlinedthe underlying principles of the transformer, we maypro-- ceed, by wayof .further exposition, to' construct the diagram of. a telephonichigh-potential transformer or induction-coil such; as is in standard useby the American Telephone and Telegraph Company. I Fig. 1 is a polardiagram of such a coil. The solid lines indicate secondary on shortcircuit, thebroken lines the same coil with eight thousand ohmsin'secondary circuit.

The constants of-the coil are-taken as fol- Each vector is assumed torepresent maxi mum values. :Let us consider the secondary on shortclrcuit, the primary current as one ampere, flowing through an, averageresist-L ance, .including the transmitterof, say, ten ohms, representedby O A and O H, res ectively., It is desired to know what wil be theelectromotive force and the current in the pedance, and theelectromotive force necessary to maintain thegiven current in the pri-'mary. Attacking the problemgeometricall wedraw a line O A to representthe va ue of thefharmonic primary current flowing through'a circuit-ofresistance H and secondary, how this secondary current as. v fects theprimary, What is the primary imis closed, a current ilows which actsinduct;

inductance H J. Ninety degrees behind O 1 site to the electromotiveforce of self-indue- I A we draw the line equal to 2 M I 12 m;

This line represents the electromotive force induced In the secondarycircuit by the primary current. When the secondarycircuit ively bothupon the primary and secondary circuitsj This secondary current lagsbehind t-he impressed electromotive force 0 B in the secondary, due toself-induction, by an angle 9), such that We may represent the secondaryeffective electromotive force and current by the vector O O and O D,respectively, wherein tan. 2

E2 I R2 I2 and I2 I By the graphical construction for simple circuits weknow that the right triangle 0 C B upon B as a hypotenuse represents thesecondary electromotive forces, OC representing that necessary toovercome resistance R 1 C B that necessary to overcome theself-i-nduction 2 7r n-L I,,. The relation between the primary andsecondary circuits is entirely a mutual one. A current-flowing in thesecondary induces an electromotive force in the primary, just thesame asa current flowing in the primary induces an electromotive force in thesecondary. The electromotive force set up by the secondary currentin-th'e primary is termed the back electromotive force and is ninetydegrees behind the secondary'current and equal to 2 nnMI Therefore inFig. 1 we may represent the back electromotive force by the line Q Fninety degrees behind the secondary current 0. D. Having assumed aprimary current, we have, as based thereupon, determined the secondaryelectromotive force, the secondary current 0 D, and the. backelectromotive force 0 F. It now remains to find what impressed primaryelectromotive force is required to cause the primary current to flow.Instead of having but two electromotive forces to overcome, as would bethe case for -a simple circuit, the primary electromotive force must inthis case not only overcome the electromotive force of resistance andself-induction in the primary, but also the back electromotive forceinduced in the H. The component necessary to overcome the primaryself-induction is equal and'oppotion and is therefore ninety degreesahead of the primary current and is represented by the vector II 'Jninety degrees ahead of O A electromotive force must be equal andopposite to O F and is represented by the line 0 G,

equal to 2 nnM 1 Having thus developed our diagram, the primaryelectromotive force desired is easily found, since it is the geometricalsum of the three components 0 H, H J, and O G. The resultant of O H andH J gives 0 J, and the resultant of O J and O G gives 0 K, whichrepresents the required primary impressed electromotive force, being inthe case considered about twenty-four volts and leading the current byapproximately twelve degrees.

From Fig. 1 it is readily seen that since the component of the primaryelectromotive force 0 G necessary toovercome the back. electromotiveforce due to the secondary is in the direction of the primary current 0A the effect of a current in the secondary is to divide the primaryelectromotive force into three components, which apparently reduces theself-induction of the primary and increases its resistance by bringingthe resultant electromotive force 0 K more in phase with the primarycurrent, whereby the primary current is increased and more power thusobtained. To further illustrate this point, reference is again made toFig. 1. In the case just considered,wherein the secondary of the coilwas assumed to be on short circuit, it will be noticed that theelectromotive force of self-induction in the primary was apparentlyreduced by the back electromotive force of the secondary from H J to H-X and the resistance increased from O H to O Y, while the electromotiveforce came quite into phase with the current, thus bringing the powerfactor nigh unto unity. Now let us assume the secondary to have a linein cirilo current falls from .37. ampere to .01 ampere,

the back electromotive force falls from 30.78

volts to .83 volt, as shown by O F. [The lag in the secondary is alsoreduced fro'm'about sixtyseven degrees t about one degree, with an e ualshift in the phase relation of the back e ectromotive force. shown inthe position of O G, with theresultant of O J and O G, which is K, asthe necessary impressed primary electromotive force equal to aboutthirty-three volts and leading the'current by about seventy-two degreesinstead of twelve degrees, with, a power factor pro ortionately reduced.

The ,values the various vectors just given are based upon the assumptionthat the primary electromotive force has been raised so as to maintain apower-current of one ampere in the primary and that the power factor ofthe primary remained the same as when the secondary was on shortcircuit. In practice we have a decreasing or at best a constant primaryelectromotive force to deal with. Under these circumstances backelectromotive force is proportionately reduced in value and advanced inphase. Now as the back electromotive force de' creasesin value andadvances in phase angle rent by a like angle.

the primary impedance increases in value and the impressed rimaryelectromotive force advances of lea s over the primary cur- In the. casegiven the primary impedance is increased from twentyour ohms onshort-circuited secondary to thirty-three ohms with the externalsecondary circuit as iven, and, what is more im-.

portant, the p ase angle between the primary electromotive force and theprimary current is increased from twelve degrees in,

the first instance to seventy-two degrees in the latter. With the givenrimar voltage the primary current is .re uced rom one I ampere to .72ampere, which gives us for the secondary electromotive force accordingto the equation 59.8 volts insteadof the apparent eighty volts. Theenergy 'of the primary circuit is reduced from,2 3.47 watts E I cos. 15,to 5.33 watts, with a corresponding reductionin the energy ofthesecondary circuit or main "line. .Since the magnetic field, by meansof which alone energ is transferred fromthe primary to the secon ary Theresult is pacity of a transformer, is dependent upon the value of theprimary current and its power factor and the secondary olta e isdirectly proportional to the energy oft e magnetic field, it follows,then, that any reduction in the secondary or line current as a resultofan increased resistance or length of line causes a correspondingincrease in the impedance of the primary, and therefore a reduction inthe primary current, which in turn operates to further reduce thesecondary or line current by reducing the secondary potential, which iis equal to 2 1; nM 1. Thus it is seen that to the primary impedance andsecondary resistance is due most of the inefficiency of'telephonicinduction-coils or transformers. On

account ofprimaryself-induction andhysterei sis losses it 18 imracticable to avail ourselves of a' magnetic eld ofsuflicient intensityto warrant an efficient transformation. On accountof secondaryresistance-and long-dis- 'tance telephonic lnduction-coils may be saidto operate on resistances equivalent to open .circuit-we are notallowedto take advantage of aback electromotive force which fur-' ther'reduces the transformation ratio. is true to such an extent that thetransformer This 5 referred to in Fig. 1 shows by computation a loss ofabout eighty per cent. between the primary and the secondary wattenergy, even with'the secondary on short circuit; =E I cos (iJ-E T cos.6

Having the problem stated, consider now the proposition of controllingthe primary I .self-inductmn and rendering it independent of thesecondary or line current. I have found that thiscan be done bythe useof capacity in the primary circuit, or preferably multiples thereof,whereby the primary-selfinduction maybe wholly or partially neutral-.

ized-in the given branches of the primary for any desired frequency,thus greatly increasing the primary current, and thereby the secondarycurrent in the main line. As is well known, the reactions due toself-induction. and electrostatic capacity are diametrically opposed. Ittherefore follows that for any clrcuit containin both self-induction andca it is possi le to so adjust the values of each as to make the oneneutralize the other.

When this is done, a current. will flow through 7 the circuit the same,as if it were free from any impedance whatsoever. This isthe conditionof resonance and lSPOSSlblB only when for any given period of frequency.For any periodicit above or below this the two values wi 1 notcancel-and perfect resonance will not obtain. when acircuit is maderesonant for any articular frequency-say two hundred and ty p. p. s. theeffects are experienced by all frequencies above two hundred andfifty,'but in I have found, however, that v a gradually-decreasingvalue, as will be explained later in this specification.

It is proposed to neutralize the impedance of the primary circuit bydividing the primary into two or more branched or multiple circuits andinserting a sufficient capacity and inductance into each branch ormultiple thereof to satisfy the conditions of resonance for thefrequencies to be affected, whereby larger primary currents and morepower may be obtained. Neutralizing the self-induction of the primarydoes not afiect the magnetic field of the coil or the mutual inductionupon which depends the secondary electromotive force and current. On theother hand, it enables us to obtain larger currents through theprimaries to utilize more iron in the magnetic circuit and to transformmore energy into the secondary. This will be better understood byreference to Fig. 2, which is an enlarged ortion of Fig. 1. From thisdia am it wil be seen that with the secon ary on short circuit therimary self-inoppose the reactance of se f-induction equal to the vectorJ Z. Then Which gives the same impedance for the primary as when thesecondary was on short circuit. O K becomes 0 K. The primary takespractically twice the amount of current as before and transforms anequivalent amount of energy into the secondary circuit or main line, dueto an increased ratio of transformation, and this as the result of onlypartial resonance. g

I shall consider now some numerical examples for the purpose of showingthe operation of the" general rule.

Consider a primary circuit including an induction or transmitter coil ofthe f0 lowing constants:

R external 9.5 ohms,

L .022 henry,

. 'E, 10 volts.

From the curves of Fig. 3 it will be seen that this circuit and coil,listed therein as circuit No. 4, offers an impedance of aboutthirty-four ohms to a current of two hundred and fifty p. p. s. and thatfor a frequency of seven hundred and fifty p. s. the impedance is overone hundred and three ohms.

Fig. 4 shows a series of curves of current resulting from the impedancesin the circuits given in Fig. 3 corresponding to the circuits andconstants given under the im ressed electromotive force of ten Volts..hus in Fig. 4, circuit 4, it is seen that for an impedance ofthirty-four ohms VR'EFQ'E'Q L) and a frequency of n 250 we get only .29ampere, while for seven hundred and fifty p. p. s. we get .097 ampere.This is upon the assumption of secondary on line of eight thousand ohmsor approaching open circuit. Let us introduce into the primary acapacity C. The primary impedance is then determined by the equationthen the impedance reducesto zero and the current rises to the valuegiven by I In the case under consideration this neutralization isapproximately obtained by a capacity of eighteen microfarads and theprimary current rises from .29 ampere to one ampere as a result of thiscapacity in the circuit. Reference to Fig. 3 will also show that for afrequency of seven hundred and fifty p. p. s. the current resulting fromthe partial resonance amounts to .108 ampere against .097 ampere for thesame circuit Without the capacity, thus indicating clearly the benefitsof primary resonance for telephonic currents even where the circuit isattuned or syntonized to but one frequency. Now We may divide theprimary circuit into a plurality of circuits and include in each branchthe primary of an induction-coil, together with the capacity necessaryto tune it for any given frequency, as

illustrated in Fig. 4, wherein the current values for identicalcircuits, with R and L constants the same in each, are shown fordifferent periodicities without capacity and with the circuits tuned forthe frequencies of two hundered and fifty p. p. s., three hundred andseventy-five p. s., and five hundred p. p. s., respective y. Fig. 4 alsoshows in dotted lines curves re resenting the values of current in thesecon ary circuit, wherein the secondaries are connectedin multiple,giving the vector sum of the currents in the different coils. Curve a,Fig. 4, represents the resultant of coils 1 and 2 in multiple, curve bthe resultant of 1, 2, and 3 connected in multiple into the secondarycircuit, which is considered under short circuit at a transformationratio of one to one neglecting losses. These curves are significant.

Figs. 5 and 6 illustrate the graphical method of determining the sum ofthese currents, each vector of which is drawn to a given scale representing the currents and their relative phase angles. Referring to Fig.5wherein the values are based upon a frequency of two hundred and fiftyp. p. s., it will be noted that as a result of circult 1 beingresonant'for this frequencythe current I has a value of one ampere,whereas circuits 2 and 3, representedby currents I and I owing to theirvery high impedance for this fre uency give very small-values of currentan of such relative phase relation as to but slightly increase theresultant current I I The fact is elicited, however, that for afrequency of two hundred and'fifty, only circuit No. 1 will give anymaterial current into the secondary and that though the coils are inmultiple the impedances are so great forthis frequency and the phaserelations are such that coil 1 is reinforced instead of being short-cira consequence the resultant approaches the cuited by coils 2 and 3. Nowasthe frequencies advance the currentsfrom the different coils comenearer and nearer into phase, and-as simple sum of the several currents,as illustrated by Fig. 6. These values may also be obtainedanalytically. For two coils 1n .mul-

tiple the formulafor the resultant current is I 'VE a 2 a 11- cos. 17

where aand (1 represent the value of the two currents and the phaseanglebetween them.

find the resultant of thefi'rst two, then combine this resultant withthethird, and so on shall now-give so far as may be-necessary the Forthe resultant of three or more currents for the series. I e c Havingillustrated the general theory and underlying principles upon which theresonan'eefeatures of my invention are based, I

detail of method and apparatusfor carrying thistheoryinto eflect. I

In; the art of telephony the mechanical energy of the'voice istranslated into electrical; energy through the agency of a diaphragm inoperative relation to a variable-' 1 resistance medium in closed circuitwith'a .constant potential sourcejof electrical energy and fatransformer. The; changes in the. variable resistance-following thevibrations of the diaphragmcreates' a funidirecti'onaI variablecurrentthrough the-closed circuit in.-

- eluding the-primary of "the; induction coil.

' This primary current beingunidirectional, it-

- requisite under the given denditionse-for the follows'thatqacondenser-cannot be placed in senes with vthe primary coil a necessarycircuit'being ar -constant potential one nothingeim'a *beg'ained byplacing a'condenser in multi [ebwith the primary of the coil. -Totransorm if-the primary .unidirectional {TOUT-- rent-3 iiitr 'fgari:alternatin'g secondary current for cpurpo'se of utilizingxthe-principleof in resdmfiwin th n ryfthen transferri this'icurrentto line b -mea;nsof another tram former,"involves the ossesof both transform-- ers,together with the dielectric losses of the condensers, which may morethan equalize the the esser'itia yoice equencies. These facts and thevery complex nature of the frequencies' and phase relations of a'VOICG-OUIIGIIT/ have apparently led to the belief by tele-- v i phonicauthorities that the principles of res-' onance cannot ,besuccesslvely.appliedto telephonic circuits except for the purpose ofcounteracting the capacity ofthe main line, and thereby reducing theattenuation factor of transmission. 1 have discovered a method, however,wherebya capacity maybe successfully placed in series with the rimary ofa transmitter induction coil and cies, which will be better understoodby ref gains conse uent u on a proper tuning for:

erence to Fig. 7. '-Referring to this figure, it

will be seen that we have a variable resistance 1 in series with aconstant-potential source 'of' circuit and make this branch of thecircuit 1 resonant for a given frequency. It will be noted that whilethe circuit divides at 3 and 4-into .two branches the source of energysupplying a unidirectional current can only -cause a'current to flowthrough the branc containing the variable resistance 1, the currentthrough the other branch being stopped by the condenser 6. I T his'isthenormal condltl'OIl Of thecircui-t. Consider now theresult of varyingthe resistance 1. mal conditions about ninety-eight percent.

IOO

Under nor-' Ofatlltdtfil resistance of the circuit formed.

by 1, 2,3,. and 4 lies in the variable resistance 1 itself. Thereforeninety-eight per cent. of the dropof potentialin the circuit will bebetween the )oint s. 3 -and'4, or, in

. other words, therewil- "be a difierence ofv potential between thesepoints-equivalent to ninety-eight per cent. of the potential of thebattery or'source of energy 2.

rent flows normally through the branch of the circuit containing theprimary coil 5 and condenser .6, the condenseris charged to the samepotential that exists between 3 and 4. It follows thatif the resistance1 be suddenly lowered, as is. the case with a telephonic trans While nocur-..

mitter when a sound-wave strikes the dia-' phragm thereof, the potentialbetween the oints 3 and4 is proportionatelylowered,and eing now of-alower potential than'th'e condenser 6 the condenser discharges; causinga current. toilow',.asjshownbv the arrows,

.through the? oint 4, the transmitter 1, the

point.3-, and t 1e induction-coil i'vgto the other side ofthe'condenser, audit-his current not onlyflows under apotent-ial equaltothe -9. A the circuit 1 tuned for any desired frequency or frequen-fmaximum variation of the resistance of the system, but flows through acircuit whose impedance has been neutralized or reduced by resonance topractically its ohmic equivalent and at a time when the transmitterresistance is at its minima, thus enormously increasing the availablecurrent in the primary coil 5, which in turn proportionatelycondenser-terminals, causing it to take, a maximum charge and todischarge again upon a decrease in the potential across 3 and 4, due toanother reduction in the resistance 1, and thus with each excursion ofthe diaphragm to and fro the resistance'of the trans mitter 1 isalternately increased and decreased, ra1smg or lowering the differenceof potential across the terminals of the condenser, which in beingalternately charged and discharged produces a current through theprimary coil 5. It will also be-noted that by this method an absolutelyalternating current is utilized in the primary coil, which varies from-apositive maxima through zero i to a negative maxima, thus insuringbetter transformer efiiciency and better definition of wave form as aresult of permitting the use of a greater amount of iron in the core ofthe primary coil, and the variation of the magnetic fluX'in the core ofthe coil from maxima through zero to maxima again instead of I merelyreducing the value of a magnetic flux of constant polarity from maximato a certain percentage of'itself. This is a distinct step in the art.

From the circuitstraced in Fig. 7 it is evident that points 3 and 4 maybe divided into a plurality of circuitsv each containing the primary ofan induction 'coil with the necessary inductance and capacity-requisiteto make each' branch resonant for the desired frequency.

, By winding the primaries of the inductioncoils with an increasednumber of turns the transformer efiiciency'm'ay not only be increased,but the inductance of the primary coil itself may largely serve totune-the circuit. It is probably advisable, however, to insert separateinductances in the circuits, so as to use the largest amount ofinductance in the primary circuit that is practicable without undulyincreasing its resistance, for the reason that by. so doing smallercapacities will berequired for the necessary tuning, and reliablecondensers are not only cumbersome and bulky, but also very expensive.

tive force in atransformer. As stated in the' As has been stated in theforegoing, a circuit is tuned or made resonant for a given frequencywhen n 2 nc then by transposition .80

As inductance 1s a factor which has to be dctermined ordinarily bycomputation, the expression therefor 18 here given, which is t number ofturns in the coil.

A-area of magnetic core in square c. In. cross-section.

z mean length magnetic circuit.

,u permeability of iron core.

In this connection it should be stated that satisfactory results are tobe obtained in tuning forrcsonance only by the use of mica or aircondensers, as I have found by disappointing and painstaking experimentsthat paraflin condensers are not to be relied upon, owing to dielectrich steresis and low insulation, which varies within wide limits withchanges of temperature.

Having now covered the several fundamental elements of my systementering into the application of resonance principles to the primarycircuit for any desired frequency or frequencies and the method ofproducing the same, I shall now advance to the next step in thedirection of increasing the effective main-line potential, so as to givea maximum line-current.

As is well known, in order to-efl'ect the long-distance transmission ofa telephonic transmitter-current it is necessary to step up thelow-potential current of the primary; but there is a limit in thusobtaining the necessary main-line potential, beyond which we may not goand wherein much is lost to telephony. To throwlights upon this point,let us briefly consider the secondary electronic- I2 5 foregoing, thiselectromotive force is equal to the primary electromotive force multilied by the ratiooftransformation. This, ow-

.ever, is not all, for the electromotive force so obtained is merely anapparent electromo- I3 may be expressed as lows that the coefficient ofself-induction, being y proportional to the square of the number ofturns we may say that y=%*,approXimatelyel This leads us to considei'the fictitious nature of the secondary electromotive force so obtainedas affecting secondary cur rent. By derivation we may determine the"secondary current in general by the equation The denominator in thisequation .shows us the limitations; of transformation for efiectivesecondary. potential.

not only shows us that the a parent second Furthermore, it

ary-potential must be divide by the seconds ar'y impedance, but thatftheprimary resistf' ance is a factor transferred .to the-secondary j andthat the transformation ratio is" also a factor, in the divisor whichincreases [as the .si1uare,.while; the secondary resistancein-x creasesd1rectly. To illustrate, con'slder a 60 ohms, From the equation we wouldget-a certain secondary current. r Suppose the sec-jondary turns t bedoubled, or made four thou- 5 sand eight hundred, what would'be theres'ult2It is'qadmitte'd that we should, obtain an apparent secondarypotential oftwfice the .-';01 iginal value; butsince We have increasedthe-secondary resistance to one hundred and Y 14 1 .it readily seentwenty ohms and the square of the. trans- .by substitution" that so,fares-secondary current is concernedi we have lost' by'the OPGIMDIOHL'T1118, is one heretofore meant U a I which resulted inagreater drop ofpotential 1 reason-why telephonic transformers have not been operated ona transformatlon rat o be- *yond a certain vmoderate value. Anotherreason is that a hi h transformation ratiehas iigh secondary impedance,

.' across the secondary terminals than across .the receiver terminalsconsidering the re- I ceiv'ing station or. terminal.- of the c rcuit 1not only. reduces theefiectivekcurrent 6,6

through 'thei' receiver, thus impairing the transmission; but' ser1ouslyinterfereswith theyoiee harmonics or overtones "as a result if nf-wavereflection and. dissymmetryjiof wave f 'preipa'gation, due-tothepQs'ition of. the secn ary' impedance in-relation to the receivercuits for larger currents, which in the circuit, and it is war known. bytelephone engineers that by shunting out .the

secondary of high potential coils the efii ciency of the receiver israised by fifty per cent. or more. This again refers us to and accountsinpart for thelow-efi'iciency transmitter induction-coils in general useon the long-distance lines of the American Telephone a and TelegraphCompany. Now in my invention the essential efiective transformationratio is obtained by tuningthe fprimary cir-' om the expression forsecondary electromotive. force, E =2 7: ,n M 1,, gives us the sameresults as would begob tained by increasing the mutual induction M byraising the transformation ratio. Moreover, this is done without interfering with the efficiency of the receiver.

placing. the secondaries of the plurality of primary circuits alreadyreferred to in multiple and relating them to compensating transformersthe terminal impedances of theline m'ay be reduced to practically zeroand the receiver efficiency improved by about one Inv addition to thisIhave discovered that'by 9 hundred per cent. This will be betterunderstood by reference to FigsfS and 9.

. Referring now'to Fig. 8, let us consider the.

alternator 10 as the'equiv'alent of the second- I ary sourceofelect'romotive force 10 in Fig. 9 and that 10 is another generator atthe posed to be generating an electromotive is-, tant end of the circuitsimilarly arrange'd,the rest of 8 being identical with 9 and 4 -withsimi ar indices 'Alternator 10 is sup- IOO force, which is consideredatthe mome'nt when the current is in a positive direction" following thearrows; Thetransr'ormersT1? formatidnratio of one to one ,withorie hunedred per cent. efficiency,- ondary turns wound 'toge rection of thearrows. Upon reaching the,

plrlmary and sec t er-on the same core and connected as shown in thediagram Consider now the current flowing in theldi and it,- are taken asidentical with a trans IlIO terminal -.12.-.of" transformer T1 it passesthrough the'line-coil ,or primary in a directionaround the coi'e,.--asshown, creating a.

magnetic flux through the core. and an in-' duced electromotive force inthe other or secondary which. flows in the opposite direction around-thecore of the transf former and into theline at 14. "A similar actiontakes place in transformer n;- which generates an electromptive force inits sec 'onda in the same fdlrection as thatin the .secon ary of T 3,'which 'on account .of the two secondaries/being connected places these,I two secondaryelectromotiveforces series.

Now it is evidentthat the current from gen;

erato'r- 10 u on reachingldhais twoipaths',-the

one throng the, main-circuit and the. gener hater 1O""and the otherthrou h theme secondaries'1 5 and 1 6. It is also -fobiziousthat thesecondary paththrough windings 5-"and 13 55 tional symbo 16 isimpassable, because this path contains an electromotive force of itsown, due to muelectromagnetic force in coil 13 and itself produces acurrent which is placed in multiple with the current in' the lineprimary. In addition to this it is evident that secondary tential twiceas great as that in the main a current is also forced back through theprimary (foil 13 and the generator 10 and the potential of the generatorreduced in the main 1 line by half. its former value. Reversing thediagram and considering as the generator and 10 as the other terminal,we shall also reverse the status of the system, and the potentialthrough the circuit between 11 and 12 and through generator-10 will betwice that given by generator 10'. These resultsare of course predicatedupon ideal relations and efficiencies and in actual practice would bemodified by the losses in the transformers '2 5 and the relative valuesof transformer and generator .constants. Thus it is seen that by the useof compensating transformers we may raise orlower the line voltage or byproperly adjusting the transformers or their 0 constants oftransformation we may maintain the original potential of the source,while reducing its internal impedance to incoming "currents as a resultof the shunt to incoming currents through coils 15 and 16. It

3 5 should be observed, however, that incoming.

currents are not only shunted in multiple with the source 10, but areraised in potential to twice' that of generator '10, thus reducingtheimpedance of the terminal from two causes, and thereby increasing thecurrent through the circuit. It will be noted that I have shown anddescribed two compensat' transformers'in relation to the source 0electromotive force-one on each 5 side thereof.- Now this is notessential, and in practice one transformer properly adjusted as toconstants and transformation ratio so as to equal the line electromotiveforce is found preferable, as shown at B in Figs. 9,

5o 10, and 11'. Both methods, however, are effective and have advantagesvarying with circumstances. brings me to Fig. 9,

' "which is a diagrammatic representation of a local batt tyrile1 of mysystem in convens, w 'ch will be readily under stood, From this figure,where similar'references indicatesimi ar parts at each terminal of theline, it will beseen that the rinci- .ples disclosed and explained withre erence to Figs. 7 and '8 are applied to the operation of lieferringnow toFig. 9 specifically, A and B are the two distant terminals of theline. any approved type. 2 isa source of constant potential in-circuitwith transmitter 1, de'

coils 1 5 and 16 being in series and of a po-- 1 is a telephonictransmitter ofrived from which, branching from points 3 and 4, are twobranch circuits containing inductances L and T1,, primary coils 5 and 7,

.and capacities 6 and 8. This is identical with 7, already explained,whereby primary coils 5 and 7 are made resonant for the desiredfrequencies, as disclosed and illustrated in the fore oing. Now primarycoils 5 and 7 act by in riction upon secondaries 9 and 10 setting uptherein electromo tive forces which act upon thecompensator-transformers Tr, and Tr, in the manner previously describedin reference to Fig. 8, which is identical with the secondary terminalsystem of Fi 91 Therefore we have a system whereby the transformerefliciency is increased by resonance one hundred per cent.

or more, while at the same time neutralizing the effective impedance ofthe equivalent secondaries, and thereby increasing the sensitiveness ofthe receiver 19 by one hundred per cent., making a net gain over oldmethods of at least two hundred per cent., as verified by myexperiments.

Figs. 10 and 11 are diagrammatic re resentations of central energy orcommon attery types of my system with distant termi nals A and B andcorresponding central offices C O, which will be readily followed fromwhat has already been disclosed and a knowledge of common batterysystems in general. Like indices refer to like or e uivalent parts inFig. 9. Fig. 11 is a modification of Fig. 10, showing the method ofapplying the principles of my invention to subscribers sta-Q tions in acommon battery system instead of at the central office, as under somecircumstances may be desirable.

The apparatus is not claimed herein.

This case is filed as a divisional application of my former a plication,entitled Art of telephony, filed July 23, 1904, Serial No. 217,846,pursuant to a requirement by the Patent Oflice so as to separateapparatus and method claims.

It will be obvious that many changes and variations can be made in thedetail of my system without departingfrom the spiritvof my invention.

Therefore, without limiting myself to the details shown, what I claim,and desire to secure by LettersPatent of the United States, ls

I 1'. The ste in the art of the electrical transmission .an reproductionof sound which consists in making the terminal transmitter circuit orcircuits wholly or artially resonant for the essential frequencles to betransmitted, thereby increasing the efliciency of transformation, andthe energy transferred to the secondary circuit, substantially as setforth.

2. The step in the art of the electrical trans mission of sound whichconsists in attuning the terminal or transmitter circuit for theessential current frequencies to-be transmitted, thereby increasingtheprimary current and mission an of the terminal or transmittercircuits to .a

condition of resonance and consonance for the essential currentfrequencies to betransmitted, thereby increasing the efficiency oftransformation, and the energy transferred to the main line, and theintensity of the sound reproduced, substantially as set forth.

4. The ste inthe art of theelec'trical transmission an reproduction ofsound which *consists in making the terminal primary and secondarycircuits wholly or partiallyconsonant for the essential frequencies to'be transmitted, thereby increasing the eflicienc'y of 4 resistance,inductance and capacity'of' the.

, transformation, the potential the second-.

transformation and'tra'n'smission, andreproduc'tion, substantially asset forth. 5'. The step in the art of the electrical transmissionand'reproduction of sound=waves Wl'liCh'OOIISiStS in adjusting theconstants of primary-circuit or .circuits, so as to decrease the pr maryimpedance and increase the primary current, thereby increasm the ratioof ary and the intensity of the transmitted sound-waves, substantiallyas set forth.

6. The step in the art 'of the electrical trans- "mission andreproduction of sound, or voice,

waves WlllCll' consists 1n lncreasing the. who

. of transformation and the line-potential. by

the efficiency of reproduction, substantially electrical consonance,while reducing the terminal lmpedance to IDCOIDlIlgSOIIIld or voicewaves, and thereby'increasing the line-current and the s'ensitiveness ofthe receiver and as set forth. I

- 7. In'the art 'ofthe electrical transmission and reproduction ofsound, the method of producmg'resonance in the transmitter circuit, orcircuits, which consists in, placing the primary coil in a derived"circuit, properly tuned as 'to inductance and c'a acity," betweenpoints of variable potentia dueto variations in the resistanceof thetransmitterline, substantially as set electrodes; whereby the capacityis charged and discharged through the said primary coil with increaseand decrease of resistance in the transmitter, substantially as setforth.

" 8'. In the art of the electrical transmission and 'reproductionofsound, the method of tuning for the essential voiceor sound fre-.quencies, which consists in placing the pri- 'marycoils, in series withcapacities, in shunt" or derived circuits between points whose potentialvaries as a function of the vibration of the transmitter-diaphragm, andin adjust ing the constants of the said shunt or derived circuits toresonance for the desired frequencies, whereby a current 'is'lcaused toflow through the said primary-coils, due to the charging anddischarginggofithe said capaciv ties with increase and decrease ofpotential.

across. the terminals'of-the said shunt or derived circuits,substantially as set forth. i

In the art of the electrical transmission and reproduction ofs ou'nd,the method of,

producing an alternating current in the primary coi which consists inlacing the primary coil and acapacityin a erived or shunt circuitbetween points whosepptential varies ;as a function of the vibration ofthe transmitter-diaphragm, wherebyf aifiilte'rnating cu'rrent is causedto flow throughithe said primary coil due to the chargingand discharging of the said capacityfas the potential varies across. the terminalsof the said derived or shunt circuit,'substantially. as set forth.

10; In the art of the electrical transmission and reproduction of soundbymeansof electrical waves, the method; of improving wa've definitionand characteristicsmhich consists in generating alternating currents inthe primary coil with positive and negative maxima and zero values,whereby the range of variation of the maignetic flux in the magnetic.circuit of the co is greatly increase ,and the wave form,-'definitionand quality materially inifi'oved', substantially as set forth. v

testimony whereof [have signed my name tothis specification in thepresence of r two subscribing witnessses;

.. D.1MAOLAUCHLINFIHERRELL.

, Witnesses: p GEQT. CAREY, f M. 0. KING.

